As one of processes for manufacturing a semiconductor device such as DRAM (dynamic random access memory), a substrate processing process is performed to form a film on a substrate using plasma. The substrate processing process is performed by a substrate processing apparatus which includes: a process chamber where a substrate is processed; a substrate support for supporting the substrate in the process chamber; a variable impedance electrode installed in the substrate support; an impedance adjusting unit connected to the variable impedance electrode and configured to adjust an impedance; a plasma generating unit configured to excite a process gas supplied to the process chamber; and a control unit for controlling at least the impedance adjusting unit.
When the substrate processing process is performed by the substrate processing apparatus, the process gas supplied into the process chamber is excited by the plasma generating unit, and active species of the excited process gas are supplied to the substrate so as to form a film on the substrate. At this time, as the impedance adjusting unit adjusts the impedance value of the variable impedance electrode, an amount of excited active species drawn toward the substrate is adjusted to control a film forming rate.
However, since power supplied by the plasma generating unit has a high frequency, an impedance of the variable impedance electrode for a certain impedance value adjusted by the impedance adjusting unit may be changed depending on the locations of the surface of the substrate. As a result, the electrical potential of the processed surface of the substrate may be changed depending on the locations on the surface of the substrate, the amount of excited active species drawn toward the substrate may be changed depending on the locations on the surface of the substrate, and the uniformity in amount of excited active species drawn toward the locations of the substrate may be changed at each process.
Furthermore, the uniformity of the film formed on the substrate may be changed even by a processing pressure. Thus, when a parameter such as the type of the process gas was changed, the processing pressure is changed to cope with the parameter change. However, the range which can be controlled only by the process pressure is so narrow that there is a limitation in acquiring a high film forming rate.